GB2206762A

GB2206762A - Sub-sea cable location apparatus

Info

Publication number: GB2206762A
Application number: GB08715225A
Authority: GB
Inventors: Robert Frederick Oxley
Original assignee: Individual
Current assignee: Individual
Priority date: 1987-06-27
Filing date: 1987-06-27
Publication date: 1989-01-11
Anticipated expiration: 2007-06-27
Also published as: GB8715225D0; GB2206762B

Abstract

A plurality of passive receiver/transmitter devices 12' are secured along the length of a submarine fibre-optic cable 10', and a movable position locating device 22 transmits an energising signal 26. The passive receiver/transmitter devices are adapted to be energised by the energising signal 26 and to transmit a coded transmission signal 28 which can be received by the movable locating device 22 and used to provide information for establishing the position of the cable. The energising signal may be electromagnetic or sonar and may be received for a time sufficient to generate a more powerful but shorter lived response. The magnitude of the signal indicates the distance of the device 12' from the locating devices 22. <IMAGE>

Description

DESCRIPTION SUB-SEA CABLE LOCATION APPARATUS.

The present invention relates to sub-sea fibre Qptic cable location apparatus.

Communication systems commonly utilise sub-sea cables to carry communication signals. Due to the expanse of water .separating some countries these cables often have to be extremely long and where conventional materials are used, e.g. copper, this may prove relatively expensive.

Since sub-sea cables are obscured from view and are often buried in the sea bed, the location of physical faults, for example breakage, is severely inhibited. The difficulty in locating a fault increases with the length of the sub-sea cable.

With conventional communication cables the location of a breakage and the subsequent position of the broken cables may be found by using position location devices which utilise an electrical signal passed along the actual cable which either reflect or transmit signals which can be received by cable locating ap2ssratus. In addition, position location devices can utilise the communication cable for their source of power to transmit a position location signal.

However, the advent of fibre-optic communication cables to increase signal quality, and reduce cost with much increased carrying capacity, presents further difficulties. Even though the length of a cable before the fault may be found by injecting light into one end of the fibre and measuring the signal reflected by the fault, difficulties still occur when trying to locate the exact position of the damaged cable, particularly since the combination of ocean currents and the initial force that caused the damage may have displaced the cable a considerable distance from its original position.These difficulties arise from the fact that fibre optics do not radiate signals and the provision of conductcrs in the fibre-optic cable in order to power position indication transmitting devices is more difficult. Fibre-optic cables are also less detectable by conventional metal detectors because they contain less metal.

Light can be injected into or extracted from a fibre-optic cable in two different ways. Firstly, it can be injected/extracted remotely, wherein light is injected into/extracted from the cleaved end of the fibre. Secondly, it can be injected/extracted locally, wherein the fibre is bent to a pre-determined radius of curvature until total internal reflection within the cable is lost and light may be injected into or extracted from the side of the fibre.

Since tapping the fibre-optic cable to provided a power source for a transmitting device would involve extracting light locally from the fibre, this method could not be employed since a relatively large amount of light signal would be lost during normal operation of the fibre-optic communication cable.

With the increasing use of sub-sea fibre-optic cables in communication systems it would therefore be advantageous if apparatus could be provided which locates the exact position of a fault or breakage of the cable. In addition, in order to protect the cable they are increasingly buried even in deep ocean beds and in these cases fibre cable location is even more difficult with conventional means.

In accordance with the present invention there is provided sub-sea fibre-optic cable location apparatus comprising a plurality of receiver/transmitter devices fixedly secured along the length of said fibre-optic cable wherein a signal received. by the receiver of the receiver/transmitter device energises the transmitter of the receiver/transmitter and further comprises movable position locating apparatus for transmitting the energising signal to said receiver/transmitter devices and for receiving the energised signal emitted from said receiver/transmitter devices.

Advantageously, the signals involved are electromagnetic signals. or sonar signals, or both.

Preferably, the position locating apparatus is provided within a single device which may be moved along near to the cable.

The position locating apparatus may be trawled from a boat and in particular from a boat from which any repair work will be carried out.

Alternatively, the position locating apparatus may advantageously be housed within a remote control miniature submarine vehicle. Such vehicles can have considerable energy sources available, the injection of energy from the vehicle into the receiver/ transmitter device being sufficient to provide the energised signal from the receiver/transmitter device at a level detectable by the receiver on the position locating apparatus.

Preferably, the signal emitted by the position locating apparatus and the energised signal received thereby have a magnitude which is proportional to the proximity of the locating apparatus to one of the plurality of receiving/transmitting devices.

Advantageously, the energising signal received by the plurality of receiving/transmitting devices is received over a period of time to provide sufficient energy for a more powerful transmission.

Preferably, each of the plurality of receiving/ transmitting devices transmits a unique coded signal which relates to its position along the cable.

The invention is described further hereinafter by way of example only, with reference to the accompanying drawings, in which : Fig. 1 illustrates the possible position of one embodiment of sub-sea fibre-optic cable of the present invertion before and after breakage has occurred; and F ie a schematic view of the apparatus of one embodiment of the present invention.

In Fig. 1 a sub-sea Fibre-optic cable 10 having a plurailny of receiving/tranwmitting devices 12, 14, 16, 18 and 20 is illustrated. Each of the devices 12, 14, 16, 18 and 20, once energised, is capable of emitting a unique signal The signal emitted by each device is ralated to its position along the cable.

.rcr example, i devices 12, 14, 16, 18 and 20 are the only dexiese located along the cable 10 then device 12 may emit a coded "1" signal, device 14 may emit a coded "2" signal, and so on, along the cable.

The sub-sea fibre-optic cable 10' illustrated as a chain dotted ine is a possible position of the cable 10 after a force has acted so as to break the cable at A. Such a force may typically be exerted by a submarne vehicle or a submarine attachment to a surface vessel.

The actual length of the broken sections may be found by injecting light at the ends of the cable and measuring the light reflected at the breakage point A. However, it will still be necessary to locate the actual position of the cable sections which may have beu influenced by other factors, for example ocean currents.

In Fig.2, a position location device 22 is trawled f-onl a boat (not shown) by an attachment 24. The device 22 travels in the vicinity of the broken cable 10' of Fig.l. An electromagnetic signal 26 is emitted downwardly towards the cable by the device 22. When the device 22 encounters one 12' of the plurality of receiver/transm.tter devices of Fig.l, the signal 26 provides the power supply for the receiver/ transmitter device 12' which is a passive device and thus the signal eergises the device 12' so that it emits an electromagnetic signal 28. The energising signal 26 is received by the device 12' for an amount of time such that the energised signal 28 emitted from the device 12' is more powerful although shorter lived than the received energising signal 26. The energised signal 28 is used as a position indication signal and is received by the device 22 having moved to position 22'. The magnitude of the signal indicates the distance of the device 22 from the receiving/ transmitting device 12'. The magnitude of the signal 28 received by the device 22 controls the magnitude of the signal emitted by the device 22 so that if the device 22 is travelling away from the cable the signal 26 will still be adequate to energise the transmitting/receiving device 12'. The position of the plurality of devices 12', 14', 16', 18' and 20' is fed back to the surface vessel (not shown) and if necessary a correction is made to the course of the vessel so that the device 22 follows the path of the displaced broken cable. Since the actual length of the broke cable is known from previous measurements, the exact location of the damaged or broken ends of the cables may be located.

Claims

1. Sub-sea fibre-optic cable location apparatus comprising a plurality of passive receiver/transmitter devices secured along the length of a fibre-optic cable and a movable position locating device for transmitting an energising signal, the passive receiver/transmitter devices being adapted to be energised by said energising signal and to emit a coded transmission signal which can be received by the movable locating device.

2. Apparatus as claimed in claim 1, wherein the signals used are electromagnetic signals or sensor signals, or both.

3. Apparatus as claimed in claim 1 or 2, wherein the signal received back by the position locating deivce from any particular one of the receiving transmitting devices is arranged to be proportional to the proximity of the locating apparatus to that receiving/transmitting device.

4. Apparatus as claimed in claim 1, 2 or 3, wherein the energising signal received by the receiver/transmitter device is arranged to be accepted by the receiver/transmitter devices over a period of time, such that the energised signal emitted by such receiver/transmitter devices can be more powerful, although shorter lived, than the received energy signal.

5. Apparatus as claimed in any of claims 1 to 4, wherein each of the plurality of receiving/ transmitting devices is adapted to transmit a unique coded signal which relates to its position along the length of the cable.

6. Apparatus as claimed in any of claims 1 to 5, wherein the position locating apparatus is provided within a single device which may be moved along near the cable.

7. Apparatus as claimed in any of claims 1 to 6, wherein the position locating apparatus is adapted to be trawled from a boat.

8. Apparatus as claimed in any of claims 1 to 6, wherein the position locating apparatus is housed within a submarine vehicle.

9. Sub-sea fibre-optic location apparatus comprising a plurality of receiver/transmitting devices fixedly secured along the length of a fibreoptic cable wherein a signal received by the receiver of the receiver/transmitter device energised the transmitter of the receiver/transmitter and further comprises movable position locating apparatus for transmitting the energising signal to said receiver transmitter devices and for receiving the energised signal emitted from said receiver/transmitter devices.

10. Sub-sea fibre-optic cable location apparatus substantially as hereinbefore described, with reference to and as illustrated in, the accompanying drawings.